DESCRIPTION: (Adapted from the application) Cannabinoids affect not only neurobehavioral but also cardiovascular functions. The neurobehavioral effects are mediated by the CB1 receptor, which is localized primarily in the brain and recognizes not only plant-derived but also endogenous cannabinoids, such as anandamide, or the selective CB1 antagonist, SR141716A. The PI has recently published observations demonstrating that anandamide elicits prolonged hypotension in anesthetized rats, which is mediated by peripherally located CB1 receptors and that activation of peripheral CB1 receptors, likely by anandamide derived from macrophages, contributes to hemorrhagic hypotension via a NO-independent mechanism. The general aim of the present proposal is to test the hypothesis that activation of peripheral CB1 cannabinoid receptors by endogenous ligands represents a novel vasodilator mechanism involved in regulating vascular tone in certain forms of shock. First, the investigators will extend findings that implicate vascular CB1 receptors in the hypotension elicited by bacterial endotoxin (LPS), by a mechanism similar to that in hemorrhagic shock. The role of CB1 receptors in LPS-induced hypotension will be further tested by the use of CB1 "knockout" mice, and the potential role of CB2 receptors in LPS-induced tachycardia will also be explored. Since both macrophages and platelets activated in vivo by hemorrhage or in vitro by LPS can elicit CB1 receptor-mediated hypotension in normal rats, but only macrophages produce detectable levels of anandamide, a second aim will be to identify the substance(s) generated by platelets that is responsible for this effect. Third, they will attempt to identify the upstream mechanism responsible for activating the endogenous cannabinoid system in hemorrhagic and endotoxic shock, with special emphasis on platelet-activating factor (PAF) and the CD14 pathway. Fourth, they will determine the relative importance of vascular vs presynaptic sympathoinhibitory CB1 receptors in shock-related hypotension. They will also use an isolated perfused mesenteric arterial bed preparation to determine the relative importance of endothelium vs smooth muscle as a target of the direct vasodilator action of anandamide. The findings of the proposed research will significantly expand our understanding of paracrine mechanisms involved in the control of vascular tone.